[Openmd-users] Doubt in creating spherical gold nanoparticle

[Dan Gezelter]

Dear Zeeshan,

  The particle builders can place molecules as well as single atoms.  They can also create core-shell or random alloys. To do this, however, they need to know information about connectivity and masses.  The connectivity can be specified in the molecule block, but the masses are normally specified in the force field file.  

You can use a Lennard-Jones force field, although purely pair potentials like LJ are usually not a great choice for metals.  Place the lines below in a file called LJ.frc (in the same directory):

------------------------------------
begin Options
      Name                   "LJ"
end Options

begin BaseAtomTypes   
// name and mass in amu: 
Au  196.97
end BaseAtomTypes

begin LennardJonesAtomTypes
// name, epsilon(kcal/mol) and sigma(angstroms):
Au  0.039  2.934
end LennardJonesAtomTypes
------------------------------------

Then you can replace your forceField and forceFieldFileName lines with:

forceFieldFileName = "LJ.frc";

(The sigma and epsilon parameters above are just a guess).

The builders should be able to use the user-defined force field file to create the particles.

 Best regards,

 --Dna Gezelter



> On Dec 23, 2016, at 12:57 AM, Zeeshan Ahmed <zeeshan.ahmed at iitgn.ac.in> wrote:
> 
> Dear openmd users,
> I have created a spherical gold nanoparticle of radius 3 nm using Openmd software (code attached). In the code I am confused on  the reason why I have to give the force field to create a nanoparticle. Can't I simply give the lattice constant to create a nanoparticle, as I will be giving the LJ pair potential value of gold-gold atoms in my script later on. What if I want to give the LJ potential for gold atoms interaction within the nanoparticle. In that case I should have to give LJ forcefield in the code instead of "Suttonchen.frc". JUst for the sake of creating a nanoparticle , can I give this forcefield and then later use the LJ forcefield in the simulation? May be due to this I am getting some weird values while I put that nanoparticle in the base fluid to find thermal properties.
> 
> I will be grateful for any kind of help.
>   
> #code
> 
> <OpenMD>
>   <MetaData>
> molecule{
> name = "Au";
> 
> atom[0]{
> type = "Au";
> position(0.0, 0.0, 0.0);
>      }
> }
> 
> component{
> type = "Au";
> nMol = 1;
> }
> 
> forceField = "SC";
> forceFieldFileName = "SuttonChen.QSC.frc";
>   </MetaData>
> </OpenMD>
> 
> # Lattice constant value of gold
> 
> nanoparticleBuilder --latticeConstant=4.08 --radius=15 gold.omd -o NP15.o
> Thanks and Regards
> Zeeshan Ahmed
> PhD Student (Mechanical)
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> Openmd-users at openmd.org
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*************************************************************
 J. Daniel Gezelter
 Professor and Director of Undergraduate Studies
 Department of Chemistry and Biochemistry
 251 Nieuwland Science Hall
 University of Notre Dame
 Notre Dame, IN 46556-5670

 gezelter at nd.edu | (574) 631-7595 | http://gezelterlab.org
*************************************************************